Processes for the ortho-alkylation of phenols are known in the art. In such a process, a phenolic compound or mixture of phenolic compounds having a replaceable hydrogen atom in at least one of the two ortho positions on the ring is reacted with an alkylation catalyst. By way of illustration, an excess of methanol is reacted with a mixture of phenol and ortho-cresol at elevated temperatures, using a catalyst, to produce 2,6-xylenol. This product is particularly useful as a monomer that can be polymerized to form poly(2,6-dimethyl-1,4-phenylene) ether, a high performance engineering thermoplastic material.
Various ortho-alkylation catalysts and methods for their preparation and use are described in the patent literature. A number of such catalysts have been disclosed by Van Sorge, including magnesium oxide (U.S. Pat. No. 3,972,828), finely divided mixtures of magnesium oxide and manganese oxide (U.S. Pat. Nos. 3,972,836 and 3,974,229), and mixtures of magnesium oxide and manganese sulfate (U.S. Pat. No. 3,873,623). The magnesium oxide in these catalysts may be derived by the thermal decomposition of magnesium carbonate.
Hamilton, U.S. Pat. No. 3,446,856 described a process for the vapor phase ortho-methylation of phenols in the presence of a magnesium oxide catalyst. As taught in column 6, beginning on line 53, the catalyst can be used in conjunction with minor amounts of other metal compounds exerting a promoting action, such as zinc oxide, lead oxide and zinc chromite. As taught further in column 6, on lines 66-69, the promoter can be used as a heterogeneous mixture throughout the catalyst bed, be coprecipitated with the magnesium oxide, or be used as a separate zone at the reactor inlet end. If coprecipitated with the magnesium oxide, Hamilton's promoter must necessarily be an initially soluble compound, although not expressly indicated in the patent disclosure. The temperatures at which the catalyst is calcined, and thus activated, are relatively high, 475.degree.-600.degree. C. (column 7, lines 21-25).